Analysis of some characteristics associated to the biopesticide activity of cured derived colonies from the Bacillus thurinqiensis native strain IBUN28.5

Abstract

Spodoptera frugiperda (J.E. Smith). is an insect pest that represents an economic loss for different agricultural crops in our country. Instituto de Biotecnología from the Universidad Nacional de Colombia, have been interested in developing some strategies for the biological control of this pest. for instance, it has been evaluating the biopesticide activity of native strains of Bacillus thuringiensis (Berliner) on thís pest insect. Into this process, it is important to remark the IBUN28.5 strain because it has a higher biopesticide activity against S. frugiperda, than the Bt subsp aisawai HD137 standard strain. In order to obtain colonies with different content of cry genes, and evaluate the role of each gene in the biopesticide activity, it was used the technique of curing plasmids. It was used acridine orange, ethidium bromide, SOS, temperature, and in some cases subculturing, like curing agents for the native strain IBUN28.5 and the standard strain HD137. The selection of the cured derivatives was made by microscopic observation, plasmid profiles, insecticidal cristal proteins profiles, and PCR analysis. Selected strains were tested in bioassay against first instar larvae of S. frugiperda, by using two concentrations of freezing dried proteins: 240 y 480 ng/cm2 Percentage of mortality was the bioassay's response. It were obtained some colonies without a plasmid of around 80 MDa to the native strain and 77 MDa to the standard strain, both plasmids have the crylAb gene. Other derivatives lost cry1Ab, cry1C, and cry1Dgenes, but it was not discovered which plasmid contains the last two genes. The bioassay results suggest that whole cured genes have an important role in the biopesticide activity of the IBUN28.5 and the standard strain Bt aisawai HD137. In addition to that, the results suggest that the difference in the biopesticide activity of both strains is because of the intrinsic characteristics of the cry1C and cry1D genes.